Technical Field
This invention is in the field of removing contaminants from diesel fuel and, in particular, the removal of particularly difficult and high pollution contaminants, such as sulfur.
Description of the Related Art
In the past, there have been few, if any, environmental regulations regarding the burning of diesel fuel by ocean-going vessels, such as large cargo ships, container ships, tankers, and luxury cruise liners. As a result, very low quality, dirty fuel has often been used in such vessels, sometimes called bunker oil or bunker fuel. Traditional bunker oil is extremely crude and highly polluting. During the refining of gasoline, higher quality fuel materials such as propane gas, gasoline for cars, and jet fuel are removed from the crude oil and the heavier petroleum products like diesel oil and lubricating oil are then removed leaving bunker oil as the last residue. The bunker oil may therefore contain a high amount of sulfur, often in the range of 3.5% and sometimes in the higher range of 4%-4.5%. Very little, if any, effort is made by the refining company to remove this sulfur from the bunker oil since this would take more time and money and raise the cost of the fuel oil significantly, with few regulations for burning high sulfur oil in a large cargo ship in the middle of the ocean, the oil is sold for this purpose. The bunker oil may also contain other pollutants which may range from lead, antimony, arsenic, styrene and other highly polluting substances.
With the rise of concern about the environment, a number of ship operators would prefer to burn a cleaner fuel and not burn a dirty, low quality bunker with its highly contaminating pollutants. Unfortunately, bunker oil is the commodity product which is widely produced in many locations in the world, and it is difficult and sometimes impossible to obtain bunker oil that does not have high contents of such pollutants, a particular problem being sulfur.
In addition, many ports are issuing regulations that limit the amount of pollutants, such a sulfur and mercury that can be burned while the ship is within the port boundaries. Some of the regulations require that the bunker oil contain less than 0.5% sulfur before it can be used to power a diesel engine within the port boundaries. Since bunker oil having such a low sulfur content is not available on the market, many ship operators must completely shut down their diesel engines when they are docked at a port and use land electric lines for powering systems on the ship which can be extremely expensive for the city to provide the high power capacity of a ship and also expensive for the ship operator to purchase the electricity.
If the ship operator were to attempt to remove the sulfur from the exhaust gas after combustion in the engine, this is not possible with the high level of pollution in most bunker oils. The traditional exhaust gas scrubber and catalytic converter in the form of an SCR normally only works when sulfur level is below 1%. Further, the higher sulfur content will clog the catalytic elements that remove NOx and render them useless for any type of pollution removal. Therefore, the option of scrubbing the exhaust gas and removal of any pollutants from the exhaust smoke stack is not a practical solution for a large cargo ship that is burning bunker oil having a high sulfur content.